Lorentz-Lorenz Coefficient, Critical Point Constants, and Coexistence Curve of 1,1-Difluoroethylene

We report measurements of the Lorentz-Lorenz coefficient density dependence, the critical temperature, and the critical density, of the fluid 1,1-difluoroethylene. Lorentz-Lorenz coefficient data were obtained by measuring refractive index and density of the same fluid sample independently of one another. Accurate determination of the Lorentz-Lorenz coefficient is necessary for transformation of refractive index data into density data from optics-based experiments on critical phenomena of fluid systems done with different apparatus, with which independent measurement of the refractive indes and density is not possible. Measurements were made along the coexistence curve of the fluid and span the density range 0.01 to 0.80 g/cc. The Lorentz-Lorenz coefficient results show a stronger density dependence along the coexistence curve than previously observed in other fluids, with a monotonic decrease from a density of about 0.2 g/cc onwards, and an overall variation of about 2.5% in the density range studied. No anomaly in the Lorentz-Lorenz coefficient was observed near the critical density. The critical temperature is measured at Tc=(302.964+-0.002) K (29.814 C) and the measured critical density is (0.4195+-0.0018)g/cc.Comment: 14 pages, 6 figures, MikTeX 2.4, submitted to Physical Review

NLTT5306B: an inflated, weakly irradiated brown dwarf

We present Spitzer observations at 3.6 and 4.5 µm and a near-infrared IRTF SpeX spectrum of the irradiated brown dwarf NLTT5306B. We determine that the brown dwarf has a spectral type of L5 and is likely inflated, despite the low effective temperature of the white dwarf primary star. We calculate brightness temperatures in the Spitzer wavebands for both the model radius, and Roche Lobe radius of the brown dwarf, and conclude that there is very little day–night side temperature difference. We discuss various mechanisms by which NLTT5306B may be inflated, and determine that while low-mass brown dwarfs (M < 35 M_(Jup)) are easily inflated by irradiation from their host star, very few higher mass brown dwarfs are inflated. The higher mass brown dwarfs that are inflated may be inflated by magnetic interactions or may have thicker clouds

Two white dwarfs in ultrashort binaries with detached, eclipsing, likely sub-stellar companions detected by K2

Using data from the extended Kepler mission in K2 Campaign 10 we identify two eclipsing binaries containing white dwarfs with cool companions that have extremely short orbital periods of only 71.2 min (SDSS J1205-0242, a.k.a. EPIC 201283111) and 72.5 min (SDSS J1231+0041, a.k.a. EPIC 248368963). Despite their short periods, both systems are detached with small, low-mass companions, in one case a brown dwarf, and the other case either a brown dwarf or a low-mass star. We present follow-up photometry and spectroscopy of both binaries, as well as phase-resolved spectroscopy of the brighter system, and use these data to place preliminary estimates on the physical and binary parameters. SDSS J1205-0242 is composed of a $0.39\pm0.02$M$_\odot$ helium-core white dwarf which is totally eclipsed by a $0.049\pm0.006$M$_\odot$ ($51\pm6$M$_J$) brown dwarf companion, while SDSS J1231+0041 is composed of a $0.56\pm0.07$M$_\odot$ white dwarf which is partially eclipsed by a companion of mass $\lesssim 0.095$M$_\odot$. In the case of SDSS J1205-0242 we look at the combined constraints from common-envelope evolution and brown dwarf models; the system is compatible with similar constraints from other post common-envelope binaries given the current parameter uncertainties, but has potential for future refinement

WD1032+011, an inflated brown dwarf in an old eclipsing binary with a white dwarf

We present the discovery of only the third brown dwarf known to eclipse a non-accreting white dwarf. Gaia parallax information and multicolour photometry confirm that the white dwarf is cool (9950 ± 150 K) and has a low mass (0.45 ± 0.05 M⊙), and spectra and light curves suggest the brown dwarf has a mass of 0.067 ± 0.006 M⊙ (70MJup) and a spectral type of L5 ± 1. The kinematics of the system show that the binary is likely to be a member of the thick disc and therefore at least 5-Gyr old. The high-cadence light curves show that the brown dwarf is inflated, making it the first brown dwarf in an eclipsing white dwarf-brown dwarf binary to be so

Spectral Analysis of Binary Pre-white Dwarf Systems

Short period double degenerate white dwarf (WD) binaries with periodsof less than ∼1 day are considered to be one of the likely progenitors of type Ia super-novae. These binaries have undergone a period of common envelope evolution. If thecore ignites helium before the envelope is ejected, then a hot subdwarf remains priorto contracting into a WD. Here we present a comparison of two very rare systems thatcontain two hot subdwarfs in short period orbits. We provide a quantitative spectro-scopic analysis of the systems using synthetic spectra from state-of-the-art non-LTEmodels to constrain the atmospheric parameters of the stars. We also use these modelsto determine the radial velocities, and thus calculate dynamical masses for the stars ineach system.Fil: Finch, N. L.. University of Leicester; Reino UnidoFil: Braker, I. P.. University of Leicester; Reino UnidoFil: Reindl, N.. University of Leicester; Reino UnidoFil: Barstow, M. A.. University of Leicester; Reino UnidoFil: Casewell, S. L.. University of Leicester; Reino UnidoFil: Burleigh, M.. University of Leicester; Reino UnidoFil: Kupfer, T.. University of California; Estados UnidosFil: Kilkenny, D.. University of the Western Cape; SudáfricaFil: Geier, S.. Universitat Potsdam; AlemaniaFil: Schaffenroth, V.. Universitat Potsdam; AlemaniaFil: Schaffenroth, V.. Universitat Potsdam; AlemaniaFil: Miller Bertolami, Marcelo Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Taubenberger, S.. Gobierno de la República Federal de Alemania. Max Planck Institut für Astrophysik; AlemaniaFil: Freudenthal, J.. No especifíca;Radiative Signatures from the Cosmos: A Conference in Honor of Ivan HubenyParisFranciaUniversidad de Pari

Pediatric brain tumor cancer stem cells: cell cycle dynamics, DNA repair, and etoposide extrusion

Reliable model systems are needed to elucidate the role cancer stem cells (CSCs) play in pediatric brain tumor drug resistance. The majority of studies to date have focused on clinically distinct adult tumors and restricted tumor types. Here, the CSC component of 7 newly established primary pediatric cell lines (2 ependymomas, 2 medulloblastomas, 2 gliomas, and a CNS primitive neuroectodermal tumor) was thoroughly characterized. Comparison of DNA copy number with the original corresponding tumor demonstrated that genomic changes present in the original tumor, typical of that particular tumor type, were retained in culture. In each case, the CSC component was approximately 3–4-fold enriched in neurosphere culture compared with monolayer culture, and a higher capacity for multilineage differentiation was observed for neurosphere-derived cells. DNA content profiles of neurosphere-derived cells expressing the CSC marker nestin demonstrated the presence of cells in all phases of the cell cycle, indicating that not all CSCs are quiescent. Furthermore, neurosphere-derived cells demonstrated an increased resistance to etoposide compared with monolayer-derived cells, having lower initial DNA damage, potentially due to a combination of increased drug extrusion by ATP-binding cassette multidrug transporters and enhanced rates of DNA repair. Finally, orthotopic xenograft models reflecting the tumor of origin were established from these cell lines. In summary, these cell lines and the approach taken provide a robust model system that can be used to develop our understanding of the biology of CSCs in pediatric brain tumors and other cancer types and to preclinically test therapeutic agents

The first sub-70 minute non-interacting WD-BD system: EPIC212235321

We present the discovery of the shortest-period, non-interacting, white dwarf-brown dwarf post-common-envelope binary known. The K2 light curve shows the system, EPIC 21223532 has a period of 68.2 min and is not eclipsing, but does show a large reflection effect due to the irradiation of the brown dwarf by the white dwarf primary. Spectra show hydrogen, magnesium and calcium emission features from the brown dwarf's irradiated hemisphere, and the mass indicates the spectral type is likely to be L3. Despite having a period substantially lower than the cataclysmic variable period minimum, this system is likely a pre-cataclysmic binary, recently emerged from the common-envelope. These systems are rare, but provide limits on the lowest mass object that can survive common envelope evolution, and information about the evolution of white dwarf progenitors, and post-common envelope evolution